The present invention relates to the field of using a bolster plate to support a circuit board, e.g., a backplane. More particularly, the present invention relates to the field of insulating the bolster plate from the supported circuit board.
Computers and their peripheral devices are used for a wide variety of purposes including, data storage, communication, and document creation. Peripheral Component Interconnect (PCI) is a local bus that is commonly used to connect a computer with one or more peripheral devices. A PCI bus provides a high-speed connection with peripherals and can connect multiple peripheral devices to the host computer. The PCI bus typically plugs into a PCI slot on the motherboard of the host computer.
CompactPCI was introduced in 1995 and has since become one of the fastest-growing industrial bus architectures to date. Initially targeted at the telecommunications and industrial control markets, CompactPCI takes the popular PCI interface and packages it into a smaller, more rugged unit. The most noticeable change made to the architecture was the adoption of a form factor in which all dimensions and mechanical components are standardized by the Institute of Electrical and Electronics Engineers (IEEE). Consequently, numerous vendors can supply mechanically interchangeable components.
One particularly interesting use of the CompactPCI is in a blade server, also called an ultradense server. Blade servers are comprehensive computing systems that include processor, memory, network connections, and associated electronics, all mounted on a single motherboard called a blade. There are many types of blades - server blades, storage blades, network blades and more.
The server blade, along with storage, networking and other blades, are typically installed in a rack-mountable enclosure that houses multiple blades that share common resources such as cabling, power supplies, and cooling fans. With its modular, hot-pluggable architecture, the easily accessible blade server offers increased computing density while ensuring both maximum scalability and ease of management.
Blade servers are smaller than traditional rack-mounted servers and have thinner Printed Circuit Boards (PCBs). These thinner server PCBs require reinforcement for attachment of central processing unit (CPU) and Central Electronic Complex (CEC) chips much like their thicker rack-mounted counterparts. CompactPCI does not allow much physical room for the necessary bolster plates or their attachment hardware. It is very difficult to pre-assemble the necessary attachment hardware to the bolster plate prior to assembling it to the blade. The bolster plates require a high stiffness that often requires that they be constructed from a metallic material.
However, because the bolster plate is a metallic and, therefore, conductive component, the bolster plate must be insulated from the server blade or other circuit board that is being supported. Otherwise, the bolster plate may cause shorts in the circuit board being supported.
In the past, layers of insulation have been secured to the bolster plate with an adhesive. However, this tends to cause a number of problems.
First, this adhesive must be flame retardant so as to prevent the possibility of being ignited by the heat and electricity of the server blade or other adjacent circuit board. Thus, it becomes necessary to identify and use a Network Equipment Building Standards (NEBS) Level 3+ compliant flame-retardant adhesive, which poses some difficulty.
Additionally, such adhesives tend to wick out of the bonded joint between the bolster plate and the insulator. The adhesive then wicks up through the vias of the server printed circuit board or other supported circuit board. This causes contamination, and potential malfunction, of the supported circuit board.
In one embodiment, the present invention provides an insulator for electrically insulating a bolster plate. The insulator includes a sheet of insulating material sized and shaped to insulate the bolster plate and at least one hole through the sheet of insulating material for accommodating a fastener for securing the sheet of insulating material to the bolster plate.
In another embodiment, the present invention provides a sub-assembly that includes a bolster plate for supporting a circuit board and an insulator for insulating the bolster plate from the circuit board. The insulator is secured to the bolster plate with one or more fasteners. Preferably, these fasteners are screws where each screw has a threaded portion, a head and an unthreaded portion between the head and the threaded portion. The insulator and the bolster plate are held on the unthreaded portion of the screw between the threaded portion and the head.
In another embodiment, the present invention provides a method of forming a sub-assembly by providing a bolster plate for supporting a circuit board, providing an insulator for insulating the bolster plate from the circuit board and securing the insulator to the bolster plate with one or more fasteners.